1. Field of the Invention
The present invention relates to a method and device for forecasting a polishing end point, and in particular, it relates to a method for forecasting a polishing end point capable of accurately forecasting and detecting a polishing end point by suppressing a joule heat loss to the minimum due to the excess current without exerting strong magnetic fluxes over an element and the like formed on a device wafer by a Chemical Mechanical Polishing (CMP) and a device thereof.
2. Description of the Related Art
There has been known a process in which, for example, an oxide film is formed on a semiconductor wafer, and the oxide film is subjected to lithography and etching, thereby to form a groove pattern corresponding to a wiring pattern, and on this, a conductive film made of Cu and the like for filling up the groove pattern is deposited, and from among this conductive film, unnecessary portion other than the filled up portion such as the groove pattern and a through hole portion and the like are removed by the chemical mechanical polishing, thereby to form a wiring pattern. In the formation of this wiring pattern, it is extremely important to put a stop to the process by accurately detecting a polishing end point when the unnecessary conductive film is removed with an appropriate thickness. When the polishing of the conductive film is excessive, a wiring resistance is increased, and when the polishing is insufficient, an insulation fault of the wiring is invited.
As the technology in this connection, for example, the following method has been known in which a change of the film thickness is monitored on the spot. This conventional technology is a method for monitoring the change of the conductive film thickness on the spot in the method for removing the conductive film from above the substrate main body (semiconductor wafer) by the chemical mechanical polishing. This method disposes a sensor including a serial or a parallel resonance circuit of an inductor and a capacitor made of a coil wound around a ferrite/pot type core for shaping in order to bring about directivity in the magnetic field in the vicinity of the conductive film, and applies a sweep output made of the frequencies of 20 Hz to 40.1 MHz from an excitation signal source to the sensor through impedance means for operation point setting. As a result, when the sensor is excited, an oscillation current flows into the coil, thereby to generate an alternating magnetic field. This alternating magnetic field subsequently induces an eddy current in the conductive film. When the eddy current is induced in the conductive film, two effects are generated. In the first place, the conductive film works as a loss resistance, and its effect is a resistance load for the sensor circuit, and this decreases amplitude of the resonance signal, and decreases the resonance frequency. In the second place, when the thickness of the conductive film decreases, an effect is generated as if a metallic rod were taken out from the coil of the inductor, thereby causing a change of inductance and a frequency shift. By monitoring a change of the frequency shift associated with a sensor resonance peak caused by the change of the thickness of the conductive film in this manner, the change of the thickness of the conductive film is continuously detected (for example, see Patent Document 1).
As another conventional technology, for example, the following eddy current sensor has been known. The literature showing this conventional technology describes as follows: quote “In general, the eddy current sensor forms an eddy current in the conductive film provided on the surface of a semiconductor substrate, and by this eddy current, the measurement of the film thickness is indirectly performed. Therefore, there arises a problem that it is difficult to perform accurate film thickness detection, whereas this conventional technology provides an eddy current sensor capable of accurately detecting the film thickness and the like from an extremely thin film to a relatively thick conductive film formed in the semiconductor substrate” unquote. To achieve this object, the conventional technology includes a sensor coil (eddy current sensor) disposed in the vicinity of a conductive film or a substrate formed with the conductive film; an alternative signal source forming an eddy current in the conductive film by feeding an alternative signal of a constant frequency to the sensor coil at the frequencies of approximately 8 to 32 MHz; and a detection circuit for measuring a reactance component and a resistance component including the conductive film, and the sensor coil includes a oscillation coil connected to the signal source, a detection coil disposed at the conductive film side of the coil, and a balance coil disposed opposite to the conductive film side of the oscillation coil, and the detection and the balance coil are connected so as to be mutually in a reversed phase. From the resistance component and the reactance component detected by the detection circuit, synthetic impedance is outputted, and from the change of the impedance, the change of the film thickness of the conductive film is detected in a wide range and approximately as a linear relation (see Patent Document 2).
Further, as another conventional technology, for example, the following eddy current sensor has been known. This conventional technology, similarly to the previous conventional technology, describes in the paragraph [0008] in the Patent Publication showing this conventional technology that the magnetic flux formed by the sensor coil penetrates the conductive film on a substrate disposed on the whole sensor coil surface and alternatively changes, so that an eddy current is generated in the conductive film, and that eddy current flows into the conductive film, thereby to cause an eddy current loss, and this is equivalent to the reduction of the reactance component of the impedance of the sensor coil when seen from the equivalent circuit. Further, the paragraph [0009] describes that when the conductive film becomes gradually thin accompanied with the progress of the polishing by observing the change of the oscillation frequency of the oscillation circuit, the oscillation frequency decreases as a result, and becomes a self-oscillation frequency of a tank circuit in which the conductive film completely disappears by the polishing, and after that, the oscillation frequency becomes approximately constant. Therefore, by detecting this point, it is possible to detect the end point of the conductive film by the chemical mechanical polishing. Further, the paragraph [0025] describes that, as shown in FIG. 2, when the polishing of the conductive film progresses, accompanied with this, the eddy current changes, and the equivalent resistance of the sensor coil changes. Consequently, since the oscillation frequency of the oscillation circuit changes, this oscillation signal is divided by a frequency dividing circuit or reduced by a subtractor, so that a signal corresponding to the size of the frequency of a detected width is displayed in a monitor. As a result, the transition of the frequency locus as shown in FIG. 2 can be obtained (see, for example, Patent Document 3).
Further, as another conventional technology, for example, the following eddy current sensor has been known. This conventional technology, in the first aspect of the invention, is an eddy current sensor including a sensor coil disposed in the vicinity of the substrate formed with a conductive film; a signal source forming the eddy current in the conductive film by feeding an alternative signal to the sensor coil, and a detection circuit for detecting the eddy current formed in the conductive film as an impedance seen from the sensor coil, and the sensor coil is an eddy current sensor stored inside a storing member formed by a high magnetic permeability material. Further, the seventh aspect of the invention discloses an eddy current senor including a sensor coil disposed in the vicinity of the substrate formed with a conductive film, a signal source forming an eddy current in the conductive film by feeding an alternative signal to the sensor coil, and a detection circuit for detecting the eddy current formed in the conductive film as an impedance seen from the sensor coil, wherein a resistance component and a reactance component of the impedance are displayed on an orthogonal coordinate axis and a film thickness of the conductive film is detected from an angle made by a straight line connecting the coordinate of the designated center point of the coordinate of the impedance (see, for example, Patent Document 4).    [Patent Document 1] Japanese Patent No. 2878178    [Patent Document 2] Japanese Patent No. 3587822    [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-21501    [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-121616